The present invention relates to a magnetic disc apparatus, such as those having a magnetic disc disposed between liner sheets in a cartridge case.
A magnetic disc obtained by forming a magnetic layer on a polymer base is called a floppy magnetic disc which is being used widely as a memory device. A prior art floppy magnetic disc is manufactured by cutting discs from a highly flexible sheet, which is formed by coating magnetic particles such as .gamma.-hematite on a polymer base with an organic binder. The magnetic disc is housed in a flat cartridge case together with liner sheets with a diameter which is equal to or greater than the diameter of the disc.
However, an attempt to increase the recording density of such a prior art magnetic disc is limited due to the magnetic characteristics of its magnetic recording layer. For this reason, new developments have been underway in recent years to form a magnetic layer by sputtering or vapor deposition on a polymer base. The layer includes a film of a metallic alloy such as Co-Cr or Co-Ni-P that has appropriate coercive force and large saturation magnetization. However, such a magnetic disc does not contain a binder in the magnetic layer. Therefore, it has a low flexibility so that the edges tend to bend or crack (rather than cutting cleanly) during the process of cutting to form a disc. The bent edge of the magnetic disc disturbs the smooth rotation of the magnetic disc during its operation since the bent edge catches on the liner sheets in the case. Also, any cracks that were generated at the time of cutting may grow. Furthermore, as the disc is used, small peeled pieces are created which produce scratches through their contact with other parts of the magnetic disc. Moreover, the bent edge creates gaps between the magnetic disc and the liner sheets which locally deform the magnetic disc, so that it results in poor contact between the magnetic disc and the magnetic head, deteriorating recording and reproducing.